Origin of pressure-induced crystallization of Ce75Al25 metallic glass

Ab initio determination of crystal stability of di-p-tolyl disulfide

With the rapid growth of energy demand and the depletion of existing energy resources, the new materials with superior performances, low costs and environmental friendliness for energy production and storage are explored. Di-p-tolyl disulfide (p-Tol₂S₂) is a typical lubricating material, which has been applied in the field of energy storage. The conformational properties and phase transformations of p-Tol₂S₂ have been studied by pioneers, but their polymorphs and the polymorphism induced crystal structure changes require further analysis. In this study, we perform the crystal structural screening, prediction and optimization of p-Tol₂S₂ crystal with quantum mechanical calculations, i.e., density functional theory (DFT) and second-order Møller–Plesset perturbation (MP2) methods. A series of crystal structures with different molecular arrangements are generated based on the crystal structure screening. As compared to long-established lattice energy calculation, we take an advantage of using more accurate technique, which is Gibbs free energy calculation. It considers the effects of entropy and temperature to predict the crystal structures and energy landscape. By comparing the Gibbs free energies between predicted and experimental structures, we found that phase α is the most stable structure for p-Tol₂S₂ crystal at ambient temperature and standard atmospheric pressure. Furthermore, we provide an efficient method to discriminate different polymorphs that are otherwise difficult to be identified based on the Raman/IR spectra. The proposed work enable us to evaluate the quality of various crystal polymorphs rapidly.

Breakdown of One-to-One Correspondence in Energy and Volume in a High-Pressure Heat-Treated Zr-Based Metallic Glass During Annealing

The glassy state of a high-pressure heat-treated Zr₅₀Cu₄₀Al₁₀ metallic glass was investigated from energetic and volumetric perspectives. The specific heat (C_p) data of initial heating and subsequent cooling from the supercooled liquid region indicates that the sample behaviour cannot be explained simply by the derivative of the well-known enthalpy (H)-temperature (T) curve. Unlike the C_p data, the thermal-expansion coefficient (α) value increased monotonically during the first heating step, which suggests the collapse of a one-to-one correspondence between the energy and volume during the process. The α data of the cooling process follow almost the same path as those of the as-cast process, whereas the corresponding C_p curves do not. This result implies that the volume appears to be more sensitive to obeying external heat compared with energy, which highlights the different time scale for achieving an equilibrium state in energy and volume. The second heating data of the C_p and α exhibit an inverse relationship against the corresponding first heating set, which confirms the breakdown of a one-to-one correspondence during annealing. The newly constructed energy-density diagram shows that the treated sample is rejuvenated volumetrically but is relaxed energetically during aging, which has never been observed experimentally previously.

Crystallization behavior of a confined CuZr metallic liquid film with a sandwich-like structure

Despite the fact that its crystal state is thermodynamically stable, Cu₆₄Zr₃₆ alloy is prone to form metastable glass at a high cooling rate. However, the confinement can induce nano-crystallization with a novel sandwich-like hierarchical structure consisting of pure Cu layers, pure Zr layers and mixed layers by conducting molecular dynamics simulations. The liquid-to-crystal transition temperature and interatomic repulsion softness display abnormal oscillations, instead of monotonous variation, as the wall-wall separation increases. When the confinement size is 10 Å and 12 Å, the transition temperature reaches a maximum, resulting from the pending new sandwich layer. The atomic movement and dynamical heterogeneity are demonstrated to play a vital role in the abnormal oscillation behavior of physical properties of the nano confined metallic glass. The sandwich-like structure can alter the Cu-Zr bond fraction, which eventually influences the liquid-to-crystal transition temperature and interatomic repulsion softness. Our findings provide a deep insight into the hierarchical nanostructures and its liquid-to-crystal transition characteristics under confinement at the atomic level.

Nanosized Gadolinium and Uranium-Two Representatives of High-Reactivity Lanthanide and Actinide Metal Nanoparticles

Gadolinium (Gd⁰) and uranium (U⁰) nanoparticles are prepared via lithium naphthalenide ([LiNaph])-driven reduction in tetrahydrofuran (THF) using GdCl₃ and UCl₄, respectively, as low-cost starting materials. The as-prepared Gd⁰ and U⁰ suspensions are colloidally stable and contain metal nanoparticles with diameters of 2.5 ± 0.7 nm (Gd⁰) and 2.0 ± 0.5 nm (U⁰). Whereas THF suspensions are chemically stable under inert conditions (Ar and vacuum), nanoparticulate powder samples show high reactivity in contact with, for example, oxygen, moisture, alcohols, or halogens. Such small and highly reactive Gd⁰ and U⁰ nanoparticles are first prepared via a dependable liquid-phase synthesis and stand as representatives for further nanosized lanthanides and actinides.

Oxygen Packing Fraction and the Structure of Silicon and Germanium Oxide Glasses

The recently proposed relationship between the oxygen volume fraction and topological ordering in solid and liquid oxide glasses at high pressure is examined with Bader's atoms-in-molecules (AIM) theory using glass structures generated from first principles molecular dynamics calculations. It is shown that the atomic (O/Si and O/Ge) volume ratio derived from AIM theory is not constant with pressure. This finding is due to the continuous change in the electron topology under compression. Unlike crystalline solids, there is no distinctive transition pressure for Si-O and Ge-O coordination in a glass; instead, the changes are gradual and continuous over a broad pressure range. Therefore, relating a unique Si-O or Ge-O coordination number to the properties of the glass at a given pressure is difficult.

Pressure-induced structural change in liquid GaIn eutectic alloy

Synchrotron x-ray diffraction reveals a pressure induced crystallization at about 3.4 GPa and a polymorphic transition near 10.3 GPa when compressed a liquid GaIn eutectic alloy up to ~13 GPa at room temperature in a diamond anvil cell. Upon decompression, the high pressure crystalline phase remains almost unchanged until it transforms to the liquid state at around 2.3 GPa. The ab initio molecular dynamics calculations can reproduce the low pressure crystallization and give some hints on the understanding of the transition between the liquid and the crystalline phase on the atomic level. The calculated pair correlation function g(r) shows a non-uniform contraction reflected by the different compressibility between the short (1st shell) and the intermediate (2nd to 4th shells). It is concluded that the pressure-induced liquid-crystalline phase transformation likely arises from the changes in local atomic packing of the nearest neighbors as well as electronic structures at the transition pressure.

Correlation between the electronic structure, topologic structure and dynamic properties of liquid cerium

We have shown an ab initio MD simulation evidence that both f-localized Ce and f-delocalized Ce can coexist in the low-density-liquid phase of Ce.